Cementing casing strings in deep water offshore wells

ABSTRACT

The present invention provides improved methods of cementing casing strings in deep water offshore formations penetrated by well bores. The methods are basically comprised of the steps of preparing a cement composition having a short transition time comprised of hydraulic cement, a water reducing additive, a dispersing additive, a compressive strength enhancing and set retarding additive, a set accelerating additive and water, placing the cement composition in the annulus between the casing string and the well bore and allowing the cement composition to set into a hard impermeable mass.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.09/353,676 filed Jul. 15, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods of cementing casing strings inwell bores, and more particularly, to methods of cementing conductor orsurface casing strings in deep water offshore wells.

2. Description of the Prior Art

In carrying out completion operations in oil and gas wells, hydrauliccement compositions are commonly utilized. For example, hydraulic cementcompositions are used in primary cementing operations whereby casingstrings are cemented in well bores. That is, a hydraulic cementcomposition is pumped into the annular space between the walls of a wellbore and the exterior of a casing string disposed therein. The cementcomposition is permitted to set in the annular space thereby forming anannular sheath of hardened impermeable cement therein. The objective ofthe cement sheath is to physically support and position the casingstring in the well bore and bond the casing string to the walls of thewell bore whereby the undesirable migration of fluids between zones orformations penetrated by the well bore is prevented.

Primary cementing operations in deep water offshore wells areparticularly difficult in that they are carried out in well bores whichpenetrate formations between the sea floor or mud line and a depthgenerally under about 2,000 feet below the mud line. Such formations areoften not well consolidated, readily fracture and often have highlypressured water flows therethrough. For example, the fracture gradientsin subsea well bores in which conductor and/or surface casing stringsare cemented limit the densities of the cement compositions utilized to11 or 12 pounds per gallon. The high water flows through the well boresoften wash away cement compositions which have densities below 10 to 11pounds per gallon.

Another problem involved in deep water offshore well cementing is thetemperature at which the cement composition must set. Deep wateroffshore wells typically have sea bottom temperatures ranging from about32° F. to 55° F. depending on the geographical location. The cementcompositions utilized for performing cementing operations at suchtemperatures must set and provide enough compressive strength to proceedwith drilling without involving long waiting-on-cement (WOC) times,preferably less than 24 hours. Accordingly, the cement compositions mustinclude set and strength accelerating agents to allow the cementcompositions to set at the low temperatures involved and develop earlycompressive strengths. However, a problem in the use of set and strengthaccelerating agents is that they often cause the cement compositions tohave thickening times which are too short to allow placement of thecement compositions in the formations or zones to be cemented. Thus, thecement compositions used in deep offshore wells must have adequatepumping times to allow placement, but at the same time they must set anddevelop sufficient compressive strengths to allow further drilling asquickly as possible. The generally accepted requirements for cementcompositions to overcome the above described problems in the Gulf Coastregion of the United States include cement composition densities in therange of from 10 to 12 pounds per gallon, thickening times of from 3 to5 hours and compressive strengths of from 400 to 600 psi at temperaturesof from about 45° F. to about 55° F.

Foamed cement compositions have heretofore been utilized in deep wateroffshore wells to obtain the low densities required. Set and strengthaccelerating agents such as calcium chloride have also been used toprovide short thickening times at the low temperatures involved. Toobtain the required compressive strengths at the low temperatures,cement blends containing at least two different cements have heretoforebeen used. For example, U.S. Pat. No. 5,571,318 issued to Griffith etal. on Nov. 5, 1996 discloses cementing compositions for use in coldenvironments which are comprised of a relatively coarse particulatehydraulic cement mixed with an ultra fine particulate hydraulic cement.U.S. Pat. No. 5,806,594 issued to Stiles et al. on Sep. 15, 1998discloses foamed cement compositions containing calcium sulfate cementand Portland cement.

API oil well cements are generally used in deep water offshore wells,and frequently, different classes of such cements must be used forcementing at different depths due to the temperature differences. Theuse of two or more different cements, for whatever purpose in drillingan offshore well, requires multiple cleanings of the bulk cement tankslocated at the drilling rig platform as well as numerous trips toon-shore blending facilities for transporting the different cements tothe platform. Thus, there is a need for a cement composition containinga single cement which can be used for cementing at various depths in anoffshore well. The use of such a cement composition would be highlyeconomical as well as environmentally preferable.

Another problem associated with offshore wells involves the use of dryadditives such as set and compressive strength accelerating agents, setretarders, dispersing agents and the like in the cement compositionsused. The use of dry additives requires the cement to be dry blendedwith the dry additives on-shore and the resulting blend to betransferred to the offshore platform where the dry blend is mixed withseawater. The blends can generally be used only for cementing at certaindepths due to the differences in temperatures, fracture gradients andwater flows. As a result, unused portions of specific cement blends haveto be discarded and replaced with newly prepared blends. Again, thisprocedure wastes time and money in that it involves additional tripsbetween the on-shore blending facility and the drilling platform. etc.

Thus, if only one basic cement is utilized and if the various additivesare added in liquid form to the mix water or slurry on the offshoreplatform just prior to cementing, the bulk-cement inventory will belimited to one dry cement on the platform that can be used throughoutthe completion of the well, decisions on the precise nature of thecement composition to be used can be deferred until it is time to beginthe cementing process and the operator will use only as much cement andliquid additives needed without generating costly waste and lost time.

Another problem which has often heretofore been encountered in deepwater offshore well cementing is the inflow of formation fluids, e.g.,water, gas and/or oil, into a cement composition which has been placedin the annulus between a casing string and the walls of a well bore, butwhich has not yet set. Such inflow of formation fluids is generallycaused by the cement composition becoming partially self-supporting andthe consequent loss of the ability of the cement column in the annulusto transmit hydrostatic pressure. When the pressure exerted by thecement composition falls below the pressure of formation fluids, theformation fluids enter the annulus and flow through the cementcomposition whereby flow channels are formed therein which remain afterthe cement composition is completely set.

The loss of the ability of the cement column to transmit hydrostaticpressure can result from the cement composition having too long atransition time, i.e., the time interval between when the cementcomposition begins to develop static gel strength and when the cementcomposition has sufficient gel strength to prevent the inflow offormation fluids. At the low temperatures encountered in offshore wells,it has heretofore been difficult if not impossible to shorten thetransition times of cement compositions enough to eliminate formationfluid inflow and the problems associated therewith.

Thus, there are needs for improved methods and cement compositions forcementing casing strings in offshore well bores whereby formation fluidinflow is prevented.

SUMMARY OF THE INVENTION

The present invention provides improved methods of cementing casingstrings in deep water offshore formations penetrated by well bores whichmeet the needs described above and overcome the deficiencies of theprior art. The methods of the invention basically comprise the steps ofpreparing a cement composition comprised of a hydraulic cement, a waterreducing additive comprised of a sulfonated naphthalene-formaldehydecondensate, a dispersing additive comprised of the condensation productof acetone, formaldehyde and an alkali metal bisulfite, a compressivestrength enhancing and set retarding additive comprised of a copolymerof acrylic acid and 2-acrylamido-2-methylpropane sulfonic acid, a setaccelerating additive and water present in an amount sufficient to forma pumpable slurry; placing the cement composition in the annulus betweena casing string and a well bore; and allowing the cement composition toset into a hard impermeable mass.

Depending on the temperature of the well being cemented and the level oftricalcium aluminate in the particular hydraulic cement used, additionalcalcium aluminate can be included in the cement composition to helpshorten the cement composition transition time. When a low densitycement composition must be used to prevent fractures from being formedin subterranean formations penetrated by the well bore, the abovedescribed cement composition can be foamed, i.e., it can include a gasin an amount sufficient to foam the cement composition and a mixture ofcement composition foaming and foam stabilizing surfactants in aneffective amount.

With the exception of the cement and the gas utilized to foam the cementcomposition, all of the other components of the cement composition canbe in liquid form.

It is, therefore, a general object of the present invention to providean improved method of cementing casing strings in deep water offshorewells.

A further object of the present invention is the provision of methods ofcementing casing strings in deep water offshore wells utilizing a cementcomposition comprised of a single hydraulic cement, mix water and otheradditives which can all be added to the mix water or cement slurry inliquid form.

Other and further objects, features and advantages of the presentinvention will be readily apparent to those skilled in the art upon areading of the description of preferred embodiments which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides an improved method of cementing a casingstring in a deep water offshore formation or zone penetrated by a wellbore using cement compositions comprised of a single hydraulic cementand other components which can all be added to the mix water or cementslurry in liquid form. The cement compositions of this invention can beutilized over a broad temperature range, e.g., from about 32° F. toabout 80° F. by simply changing the weight ratio and quantities ofcertain of the components in the compositions. Further, the cementcompositions can meet the generally accepted requirements for cementingcasing strings in deep water offshore wells, namely, a cementcomposition density in the range of from 10 to 12 pounds per gallon, athickening time of from 3 to 5 hours and compressive strengths of from400 psi to 600 psi at 45° F. to 55° F. The methods allow the operator ofan offshore platform to keep a single dry cement in bulk storage on theplatform along with the other components of the cement composition whichexcept for the gas utilized to foam the composition can all be in liquidform. The liquid components can be added to the single cement just priorto cementing whereby the operator uses only as much dry cement andliquid components as are needed without generating waste and losing timeby changing cements, etc.

As mentioned, the methods of the present invention are particularlysuitable for cementing conductor and/or surface casing strings in deepwater offshore formations or zones penetrated by well bores. The cementcompositions of the invention can be used in shallow high water flowformations in which conductor and/or surface casing strings are cementedas well as in the deeper, warmer formations in which other casingstrings or liners are cemented. Generally, the cementing compositions ofthis invention can be utilized for cementing wells at depths from 0 to8,000 feet or deeper.

An improved method of this invention for cementing a casing string in adeep water offshore formation or zone penetrated by a well bore isbasically comprised of the following steps. A cement composition isprepared comprised of a single hydraulic cement, sufficient water toform a pumpable slurry, a gas present in an amount sufficient to form afoam, a mildly set retarding mixture of cement composition foaming andfoam stabilizing surfactants present in an amount sufficient tofacilitate the formation of and stabilize the foam, a cement setaccelerating additive and a mildly set retarding cement water reducingadditive or cement dispersing additive, or both. The cement setaccelerating additive and the mildly set retarding cement water reducingadditive or cement dispersing additive, or both, are present in a weightratio and in an amount such that the cement composition has a requiredthickening time, generally in the range of from about 3 to about 5hours, and develops adequate compressive strength, generally in therange of from about 400 psi to about 600 psi, at a temperature in therange of from about 45° F. to about 55° F. within a time period of 24hours or less. Upon being prepared, the cement composition is placed inthe annulus between the casing string and the well bore, and the cementcomposition is allowed to set into a hard impermeable mass therein.

It has been discovered that aqueous cement compositions formed with APIClasses A, C, H and G Portland or equivalent hydraulic cements can bemade to have very short transition times (sometimes referred to as“right angle set cement compositions”) by including certain additives inthe cement compositions. Further, if the hydraulic cement used is notone of the high activity types, but instead is a low activity cementhaving a low content of tricalcium aluminate, calcium aluminate or oneor more alkali metal aluminates can be added to the cement along withthe other additives to achieve a short transition time. Calciumaluminate has the general formula (CaO)_(n)(Al₂O₃)_(m) where the valuesof m and n are such that the amount of CaO in the calcium aluminate canvary from about 20% to about 40% by weight and the amount of the Al₂O₃can vary from about 60% to about 80% by weight. Commercial calciumaluminates can also contain varying amounts of metal oxide impurities.Calcium aluminate is insoluble in water while alkali metal aluminatessuch as sodium aluminate are soluble in water and can be dissolved inwater prior to use offshore.

An improved method of this invention for cementing a casing string in adeep water offshore formation penetrated by a well bore whereby theinflow of formation fluids into the annulus between the casing stringand the walls of the well bore and into the cement composition thereinis prevented is comprised of the following steps. A cement compositionhaving a short transition time is prepared comprised of a hydrauliccement, a cement water reducing additive, a cement dispersing additive,a cement compressive strength enhancing and set-retarding additive, acement set accelerating additive and water present in an amountsufficient to form a pumpable slurry. The prepared cement composition isplaced in the annulus and then allowed to set into a hard impermeablemass therein.

The cement water reducing additive, the dispersing additive and thecement compressive strength enhancing and set retarding additive worktogether to reduce the amount of water in the cement composition, retardthe set of the composition and increase the compressive strength of thecomposition when set. The amount of set accelerating additive in thecomposition moderates the set retardation and the compressive strengthof the composition. The additives also function to de-agglomerate thehydraulic cement in the composition, i.e., to break up agglomeratedcement particles in the composition into separate particles whichincreases the cement surface area whereby the cement hydrates faster andprovides early cement composition compressive strength at lowtemperatures.

When a low density cement composition is required, a gas in an amountsufficient to form a foam and a mixture of cement composition foamingand foam stabilizing surfactants can be included in the above describedcement composition. Also, as mentioned above, if the hydraulic cementused is a low activity cement or if a very short transition time isrequired, calcium aluminate or one or more alkali metal aluminates canbe added to the cement composition together with the other additivesdescribed above to bring about the desired short transition time.

The single hydraulic cement preferred for use in accordance with thisinvention is one of API Classes A, C, H and G Portland or equivalenthydraulic cements. The above mentioned API cements are defined anddescribed in API Specification For Materials And Testing For WellCements, API Specification 10, Fifth Edition, dated Jul. 1, 1990 of theAmerican Petroleum Institute. The API Portland cements, or other cementswhich are equivalent thereto, are suitable for cementing deep wateroffshore wells from 0 to 8,000 feet when used with the other componentsof the cement compositions of this invention.

The water in the cement compositions can be fresh water or salt water.The term “salt water” is used herein to mean unsaturated salt solutionsand saturated salt solutions including brines and seawater. The water isgenerally present in the cement compositions in an amount sufficient toform a pumpable slurry, and more specifically, in an amount in the rangeof from about 34% to about 40% by weight of cement in the cementcompositions.

When a cement composition of this invention is foamed, the gas utilizedcan be air or nitrogen, with nitrogen being preferred. The gas isgenerally present in an amount sufficient to foam the cement compositionto a density in the range of from about 10 to about 12 pounds pergallon.

A mildly set retarding mixture of cement composition foaming and foamstabilizing surfactants which is particularly suitable for use inaccordance with this invention is comprised of a mixture of

an ethoxylated alcohol ether sulfate surfactant of the formula:

H(CH₂)_(a)(OC₂H₄)_(b)OSO₃M⁺

 wherein a is an integer in the range of from about 6 to about 10, b isan integer in the range of from about 3 to about 10 and M is an alkalimetal or ammonium,

an alkyl or alkene amidopropylbetaine surfactant having the formula:

R—CONHCH₂CH₂CH₂N⁺(CH₃)₂CH₂CO₂ ⁻

 wherein R is a radical selected from the group of decyl, cocoyl,lauryl, cetyl and oleyl and

an alkyl or alkene amidopropyl dimethylamine oxide surfactant having theformula:

 R—CONHCH₂CH₂CH₂N⁺(CH₃)₂O⁻

 wherein R is a radical selected from the group of decyl, cocoyl,lauryl, cetyl and oleyl.

The ethoxylated alcohol ether sulfate surfactant is generally present inthe mixture in an amount in the range of from about 60 to about 64 partsby weight; the alkyl or alkene amidopropylbetaine surfactant isgenerally present in the mixture in an amount in the range of from about30 to about 33 parts by weight; and the alkyl or alkene amidopropyldimethylamine oxide surfactant is generally present in an amount in therange of from about 3 to about 10 parts by weight. The mixture can becomprised of the surfactants, per se, but more preferably, the mixtureincludes fresh water in an amount sufficient to dissolve the surfactantswhereby it can more easily be combined with the cement compositionmixing water or cement slurry.

Another mildly set retarding mixture of foaming and foam stabilizingsurfactants which can be utilized is a mixture of the ethoxylatedalcohol ether sulfate described above and the alkyl or alkeneamidopropylbetaine surfactant described above. This mixture ofsurfactants is generally comprised of two parts by weight of theethoxylated alcohol ether sulfate and one part by weight of the alkyl oralkene amidopropylbetaine surfactant. This mixture also preferablyincludes fresh water in an amount sufficient to dissolve thesurfactants.

The mildly set retarding mixture of foaming and foam stabilizingsurfactants utilized is generally included in a foamed cementcomposition of this invention in an amount in the range of from about0.1% to about 3% by weight of water in the cement composition.

While a variety of cement set accelerating additives (also referred toherein as set and strength accelerating agents) can be utilized in thecement compositions of this invention, a water soluble calcium salt suchas calcium chloride, calcium nitrite and calcium formate is preferredwith calcium chloride being the most preferred. While the setaccelerating additive can be utilized directly, it is preferablydissolved in fresh water so that it can be added to the mix water orcement slurry on location. Most preferably, the set acceleratingadditive is in the form of an aqueous solution wherein the setaccelerating additive is present therein in an amount of about 33% byweight of the solution.

A preferred cement water reducing additive (also referred to in the artas a “plasticizer”) for use in the compositions of this invention is asulfonated naphthalene formaldehyde condensate. This additive allows theuse of unusually small amounts of water in the cement composition towhich it is added. The water reducing additive assists in dispersingparticles in the water to make a useful slurry at water concentrationslower than those that would normally be sufficient. The reduced waterconcentrations have the effect of increasing the compressive strength ofthe set cement. A particularly suitable sulfonatednaphthalene-formaldehyde condensate water reducing additive is describedin U.S. Pat. No. 3,359,225 issued to Weisend on Dec. 19, 1967 which isincorporated herein by reference. The additive is commercially availablefrom Halliburton Energy Services of Duncan, Okla. under the trade name“CFR-2™.”

A cement dispersing additive (which also has fluid loss controlproperties) preferred for use in accordance with this invention is thecondensation product of acetone, formaldehyde and sodium bisulfite. Thisdispersing additive is described in U.S. Pat. No. 4,557,763 issued toGeorge et al. on Dec. 10, 1985 which is incorporated herein byreference. The additive is also commercially available from HalliburtonEnergy Services of Duncan, Okla. under the trade name “CFR-3™.” Both thewater reducing additive and the dispersing additive are preferablydissolved in fresh water in an amount of about 33% by weight of thesolution.

As mentioned, the ratio of the cement set accelerating additive to thewater reducing additive or the dispersing additive, or both, and thetotal amount of such additives together in the cement composition, canbe varied to vary the thickening time and compressive strength of thecement composition at specific temperatures, e.g., a thickening time offrom about 3 to about 5 hours and a compressive strength from about 400psi to about 600 psi at temperatures in the range of from about 45° F.to about 55° F. within 24 hours. Generally, the ratio of the setaccelerating additive to the water reducing additive or dispersingadditive, or both, is varied in the range of from about 1:1to about 3:1.The amount of the set accelerating additive and the water reducingadditive or dispersing additive, or both, present in the cementcomposition is generally within the range of from about 1% to about 3%by weight of cement in the composition.

A compressive strength enhancing and set retarding additive which ispreferred for use in a cement composition of this invention is acopolymer of acrylic acid and 2-acrylamido-2-methylpropane sulfonicacid. Such an additive is described in U.S. Pat. No. 5,049,288 issued toBrothers et al. on Sep. 17, 1991 which is incorporated herein byreference. The additive is commercially available from HalliburtonEnergy Services of Duncan, Okla. under the trade name “SCR-100™.” Thisadditive is also preferably dissolved in fresh water in an amount ofabout 33% by weight of the solution.

As will be understood by those skilled in the art, in specificapplications and at specific depths in deep water offshore wells, otheradditives, preferably in liquid form, which are well known to thoseskilled in the art and which do not adversely affect the requiredproperties of the cement composition can be included therein. Examplesof such additives include but are not limited to fluid loss controladditives, viscosifying agents, thixotropic agents and anti-settlingagents.

A method of the present invention which is particularly suitable forcementing casing strings in deep water offshore formations or zonespenetrated by a well bore is comprised of the steps of: (a) preparing acement composition comprised of a single hydraulic cement, sufficientwater to form a pumpable slurry, a gas present in an amount sufficientto form a foam, a mildly set retarding mixture of cement compositionfoaming and foamed stabilizing surfactants present in an effectiveamount, a cement set accelerating additive and a mildly set retardingcement water reducing additive or cement dispersing additive, or both,present in said composition in a weight ratio and in an amount such thatthe cement composition has a thickening time in the range of from about3 to about 5 hours and develops compressive strength in the range offrom about 400 psi to about 600 psi at a temperature in the range offrom about 45° F. to about 55° F. within 24 hours; (b) placing thecement composition in the annulus between the casing and the well bore;and (c) allowing the cement composition to set into a hard impermeablemass therein.

Another method of the present invention for cementing a casing string ina deep water offshore formation penetrated by a well bore at atemperature in the range of from 32° F. to about 80° F. comprises thesteps of: (a) preparing a cement composition comprised of a hydrauliccement, sufficient water to form a pumpable slurry, a gas present in anamount sufficient to form a foam, a mildly set retarding mixture of acement composition foaming and foam stabilizing surfactants present inan effective amount, an aqueous solution of calcium chloride setaccelerating additive and an aqueous solution of a sulfonatednaphthalene formaldehyde condensate water reducing additive, wherein thecalcium chloride accelerating additive and the sulfonated naphthaleneformaldehyde condensate water reducing additive are present in saidcomposition in a weight ratio and in an amount such that the cementcomposition has a thickening time in the range of from about 3 to about5 hours and develops a compressive strength of at least about 400 psiwithin 24 hours; (b) pumping the cement composition into the annulusbetween the casing and the well bore; and (c) allowing the cementcomposition to set into a hard impermeable mass therein.

Yet another method of the present invention for cementing a casingstring in a deep water offshore formation penetrated by a well bore iscomprised of the steps of: (a) preparing a cement composition having ashort transition time comprised of a hydraulic cement, a water reducingadditive comprised of a sulfonated naphthalene-formaldehyde condensatepresent in an amount in the range of from about 0% to about 3% by weightof hydraulic cement in the composition, more preferably from about 0.3%to about 1.5%, a dispersing additive comprised of the condensationproduct of acetone, formaldehyde and sodium bisulfite present in anamount in the range of from about 0% to about 2% by weight of hydrauliccement in the composition, more preferably from about 0.1% to about0.5%, a compressive strength development enhancing and set retardingadditive comprised of a copolymer of acrylic acid and2-acrylamido-2-methylpropane sulfonic acid present in an amount in therange of from about 0.01% to about 1% by weight of hydraulic cement inthe composition, more preferably from about 0.01% to about 0.5%, a setaccelerating additive present in an amount in the range of from about0.1% to about 4% by weight of hydraulic cement in the composition, morepreferably from 0.5% to about 3% and water present in an amountsufficient to form a pumpable slurry; (b) pumping the cement compositioninto the annulus between the casing and the well bore; and (c) allowingthe cement composition to set into a hard impermeable mass therein.

Calcium aluminate or one or more alkali metal aluminates can optionallybe included in the cement composition of this method in an amount in therange of from about 0.5% to about 5% by weight of hydraulic cement inthe composition.

Still another method of this invention is comprised of the steps ofpreparing a cement composition having a short transition time comprisedof a hydraulic cement, a water reducing additive comprised of asulfonated naphthalene-formaldehyde condensate present in an amount inthe range of from about 0% to about 3% by weight of hydraulic cement inthe composition, more preferably from about 0.3% to about 1.5%, adispersing additive comprised of the condensation product of acetone,formaldehyde and sodium bisulfite present in an amount in the range offrom about 0% to about 2% by weight of hydraulic cement in thecomposition, more preferably from about 0.1% to about 0.5%, acompressive strength development and set retarding additive comprised ofa copolymer of acrylic acid and 2-acrylamido-2-methylpropane sulfonicacid present in an amount in the range of from about 0.01% to about 1%by weight of hydraulic cement in the composition, more preferably fromabout 0.01% to about 0.5%, a set accelerating additive present in anamount in the range of from about 0.1% to about 4% by weight ofhydraulic cement in the composition, more preferably from 0.5% to about3%, water present in an amount sufficient to form a pumpable slurry, agas present in an amount sufficient to form a foam and a mixture ofcement composition foaming and foam stabilizing surfactants present inan amount in the range of from about 0. 1% to about 3% by weight ofhydraulic cement in the composition, more preferably from about 0.3% toabout 1%.

Calcium aluminate or one or more alkali metal aluminates can optionallybe included in the cement composition of this method in an amount in therange of from about 0.5% to about 5% by weight of hydraulic cement inthe composition.

In order to further illustrate the methods and cement compositions ofthis invention, the following examples are given.

EXAMPLE 1

Test foamed cement compositions of this invention were preparedcomprised of API Class H Portland cement, synthetic seawater, air, amixture of cement composition foaming and foam stabilizing surfactants,an aqueous solution of a cement set accelerating additive and an aqueoussolution of a mildly set retarding cement water reducing additive. Theidentities and quantities of the various components in the test samplesare given in Table I below. The test compositions were tested forcompressive strengths at 45° F. and 55° F. after curing for 24 hoursusing Tinius Olsen loading press equipment and for thickening time at65° F. and 1,000 psi in accordance with the procedures described in thementioned API Specification 10. The results of these test are given intest I below.

TABLE I Compressive Strength and Thickening Time Tests Amount of Mixtureof Amount of Mildly Set Density of Test Mix Water in Total Water¹Foaming and Set Retarding Foamed Cement Cement in Cement StabilizingAccelerating Densifying Cement 24 Hour 24 Hour Thickening Compo-Composition, Composition, Surfactants, Additive⁴, % Additive⁵, %Composition, Compressive Compressive Time at 1000 sition % by weight %by weight % by weight by weight of by weight of pounds per Strength atStrength at psi and 65° F., No. of cement of cement of water cementcement gallon 45° F., psi 55° F., psi hr:min 1 34 37 2.25² 3 1.5 12 459535 4:54 2 34 38 2.25² 3 2 12 390 580 5:40 3 34 38 2.25² 4 1.5 12 450670 5:05 4 34 39 2.25² 4 2 12 420 630 4:57 5 34 39 1³ 5 2.25 12 495 8224:43 6 33.5 40 1³ 6 2.25 12 489 755 3:54 7 34 38.5 1³ 4 2 12 345 6825:51 ¹Water from liquid surfactant mixture and liquid accelerating anddispersing agent solutions included ²Ethoxylated alcohol ether sulfateand cocoylamidopropylbetaine ³Ethoxylated alcohol ether sulfate,cocoylamidopropylbetaine and cocoylamidopropyl dimethyl amine oxide ⁴33%by weight aqueous solution of calcium chloride ⁵33% by weight aqueoussolution of sulfonated naphthalene formaldehyde condensate

From Table I it can be seen that the test cement compositions of thisinvention meet the requirements for cementing in deep water offshorewells.

EXAMPLE 2

Additional test foamed cement compositions of this invention wereprepared comprised of various API classes of Portland cement, a waterreducing additive, a dispersing additive, a compressive strengthenhancing and set retarding additive, synthetic seawater, air, and amixture of cement composition foaming and foam stabilizing surfactants(a mixture of ethoxylated alcohol ether sulfate,cocoylamidopropylbetaine and cocoylamidopropyl dimethyl amine). Some ofthe test compositions also included a cement composition set retardercomprised of a methylenephosphonic acid derivative or mixture of suchderivatives. Such a cement composition retarder is described in U.S.Pat. No. 4,676,832 issued to Childs et al. on Jun. 30, 1987, which isincorporated herein by reference. Other of the test compositionsincluded calcium aluminate in various amounts to further shorten thetransition time. The identities and quantities of the various componentsin the test samples are given in Table II below.

The test cementing compositions were mixed at normal densities and thenfoamed to reduce the densities of the compositions to in the range offrom I0 to 12 pounds per gallon. Each of the test compositions wastested for thickening time in the temperature range of from 65° F. to150° F. A measure of the transition time for each test composition wasobtained by determining the time required for the consistency of thecement composition to increase from 30 B_(c) (Bearden units) to 70 B_(c)followed by measuring the time required for the cement composition toincrease from 70 B_(c) to 100 B_(c). The thickening time tests were runin accordance with the procedure set forth in API Specification ForMaterials And Testing For Well Cements, API Specification 10, FifthEdition, dated Jul. 1, 1990 of the American Petroleum Institute. Inaccordance with API Specification 10 A, a cement slurry is considered tohave set when it reaches a consistency of 100 B_(c). It is alsorecognized in the art that a cement slurry begins to develop gelstrength when it reaches a consistency of 30 B_(c), it is not consideredto be pumpable when it exceeds a consistency of 50 B_(c) and that acement column loses its ability to transmit hydrostatic pressure when itreaches a consistency of 70 B_(c). Thus, the transition time is the timefrom when the cement composition begins to develop gel strength (30B_(c)) to when the cement composition gel strength is strong enough toprevent formation fluid inflow (100 B_(c)).

In U.S. Pat. No. 5,806,594 issued to Stiles et al. on Sep. 15, 1998(prior art), a foamed cement composition is described having a shorttransition time, i.e., a right angle set property. The prior art cementcomposition of Stiles et al. is comprised of Portland cement, plaster ofParis (calcium sulfate), an aqueous fluid, a foaming agent and a foamstabilizing agent. Such a prior art cement composition was prepared andtested as described above for comparison purposes. The quantities of thevarious components in the test samples and the test results are alsogiven in Table II below.

TABLE II Transition Time Tests Mix Water¹ in Compressive Cement StrengthTest Compo- Development Set Time Time API Cement sition, DensifyingDispersing Enhancing Accelerating Cement Set Calcium From From Thick-Compo- Hydraulic % by Additive², % Additive³, % Additive⁴, % Additive⁵,% Retarder⁶, Aluminate, 30 B_(c) to 70 B_(c) to ening sition Cement, wt.of by wt. of by wt. of by wt. of by wt. of % by wt. of % by wt. of 70B_(c) at 100 B_(c) at Time, No. API Class cement cement cement cementcement cement cement 65° F. 65° F. hr:min 1 A⁷ 38 — 2 — — — — 72 23 2:432 A⁷ 38 — 2 0.3 — — — 45 18 4:05 3 A⁷ 38 — 2 0.4 — — — 52 16 4:24 4 A⁷38 — 2 0.5 — — — 49 16 4:50 5 A⁷ 38 — 2 1 — — — 80 19 7:14 6 A⁷ 39 1.950.65 — — — — 30 16 2:44 7 A⁷ 39 1.95 — — 1.3 — — 35 14 2:19 8 A⁷ 36 1 —— 4.0 — — 39 7 4:11 9 A⁷ 38 — 0.65 — 1.3 — — 80 17 2:43 10 A⁷ 38 1.5 0.5— 1.0 — — 27 17 3:28 11 A⁷ 38 0.5 1.5 — 1.0 — — 40 20 3:09 12 A⁷ 34 3.751.25 — 2.5 — — 17 3 4:02 13 A⁷ 38 1 1 0.1 1 — — 38 12 3:28 14 A⁷ 34 1 11.5 7 — — 22 10 3:00 15 A⁷ 34 2 1 2 5 — — 20 10 6:25 16 A⁷ 35.4 3 1 0.23.8 — — 32 9 3:24 17 A⁷ 35.4 3.62 1.21 0.17 5 — — 16 12 2:47 18 A⁷ 33.53.75 1.25 0.5 5.5 — — 24 8 2:55 19 A⁷ 33.9 3.75 1.25 0.5 4.75 — — 27 73:40 20 A⁷ 32.8 3.75 1.25 1 6 — — 20 5 3:15 21 A⁷ 34 3.75 1.25 0.8 4.2 —— 18 9 5:00 22 A⁷ 35.3 3.36 1.12 0.16 3.36 — — 25 3 4:09 23 A⁷ 36.7 2.570.84 0.12 2.57 — — — 8 3:27 24 A⁷ 34 3.75 1.25 0.25 4.75 — — 19 6 3:3825 A⁷ 38 1 1 — 1 0.1 — 55 25 3:08 26 A⁷ 38 1 1 — 1 0.15 — 25 30 4:26 27A⁷ 38 1.68 0.56 0.08 1.68 — — 45 — 6:00 28 A⁸ 38 1.05 0.34 0.05 1.55 — —55 15 4:19 29 A⁸ 38 1.68 0.56 0.08 1.68 — 1 <5 0 5:00 30 A⁸ 38 1.68 0.560.06 1.68 — 1 30 0 nd¹¹ 31 H 34 1.26 0.42 0.024 4.26 — — 60 20 4:55 32 H34 1.26 0.42 0.024 4.26 — 1 43 90 3:50 33 H 34 1.26 0.42 0.024 4.26 — 38 0 4:00 Prior C and 15.8¹⁰ — — — — — — 24 14 5.55 @ Art⁹ CaSO₄ 70° F.¹Synthetic seawater ²Sulfonated naphthalene-formaldehyde condensate, 33%solution ³Condensation product of sodium bisulfite, acetone andformaldehyde, 33% solution ⁴Copolymer of acrylic acid and2-acrylamido-2-methylpropane sulfonic acid, 40% solution ⁵Calciumchloride, 33% solution ⁶Methylenephosphonic acid derivative ⁷Cementproduced by Lehigh ⁸Cement produced by Lafarge ⁹U.S. Pat. No. 5,806,594¹⁰Density in pounds per gallon ¹¹nd means not determined

From Table II it can be seen that the compositions of the presentinvention and particularly test compositions 14, 15, 17-24, 29, 30 and33 have short transition times, all of which are shorter than thecomparative prior art test cement composition.

EXAMPLE 3

The particle size of Portland Class A cement below 10 microns wasdetermined. Thereafter, small test portions of the cement were mixedwith a few drops of the various additives utilized in the cementcompositions of this invention, i.e., a sulfonated naphthalene-formaldehyde condensate (Halliburton “CFR-2™”), a condensation productof acetone, formaldehyde and sodium bisulfite (Halliburton “CFR-3™”) andcalcium chloride. The resulting mixtures were then also tested forparticle size. The results of these tests are set forth in Table IIIbelow.

TABLE III Cement Particle Size Analysis In The Presence Of VariousAdditives Cement Cement Cement Cement With Without With With CalciumParticle Size Additive, “CFR-2 ™,” “CFR-3 ™,” Chloride, of Cement % % %% ≦1 micron 10.2 12 11.3 10.8 ≦3 microns 13 15.6 15 13.5 ≦9.93 microns26.8 34.4 33.1 29.6

From Table III, it can be seen that the additives of this inventionfunction to de-agglomerate the cement particles.

Thus, the present invention is well adapted to attain the objects andadvantages mentioned as well as those which are inherent therein. Whilenumerous changes may be made by those skilled in the art, such changesare encompassed within the spirit of this invention as defined by theappended claims.

What is claimed is:
 1. An improved method of cementing a casing stringin a deep water offshore formation penetrated by a well bore comprisingthe steps of: (a) preparing a cement composition comprised of ahydraulic cement, a water reducing additive comprised of a sulfonatednaphthalene-formaldehyde condensate, a dispersing additive comprised ofthe condensation product of acetone, formaldehyde and sodium bisulfite,a compressive strength enhancing and set retarding additive comprised ofa copolymer of acrylic acid and 2-acrylamido-2-methylpropane sulfonicacid, a set accelerating additive and water present in an amountsufficient to form a pumpable slurry; (b) placing said cementcomposition in the annulus between said casing and said well bore; and(c) allowing said cement composition to set into a hard impermeable masstherein.
 2. The method of claim 1 wherein said hydraulic cement is aPortland or equivalent cement.
 3. The method of claim 1 wherein saidhydraulic cement is selected from the group consisting of API Classes A,C, H and G Portland or the equivalent cements.
 4. The method of claim 1wherein said water reducing additive is present in said composition inan amount in the range of from about 0% to about 3% by weight of saidhydraulic cement in said composition.
 5. The method of claim 1 whereinsaid dispersing additive is present in said composition in an amount inthe range of from about 0% to about 2% by weight of said hydrauliccement in said composition.
 6. The method of claim 1 wherein saidcompressive strength enhancing and set retarding additive is present insaid composition in an amount in the range of from about 0.01% to about1% by weight of said hydraulic cement in said composition.
 7. The methodof claim 1 wherein said set accelerating additive is a water solublecalcium salt selected from the group consisting of calcium chloride,calcium nitrate and calcium formate.
 8. The method of claim 1 whereinsaid set accelerating additive is calcium chloride.
 9. The method ofclaim 1 wherein said set accelerating additive is present in saidcomposition in an amount in the range of from about 0.1% to about 4% byweight of said hydraulic cement in said composition.
 10. The method ofclaim 1 wherein said cement composition further comprises an additiveselected from the group consisting of calcium aluminate and one or morealkali metal aluminates.
 11. The method of claim 10 wherein saidadditive is calcium aluminate present in said composition in an amountin the range of from about 0.5% to about 5% by weight of said hydrauliccement in said composition.
 12. The method of claim 1 wherein saidcement composition further comprises a gas in an amount sufficient toform a foam and a mixture of cement composition foaming and foamstabilizing surfactants present in an amount sufficient to facilitatethe formation of and stabilize said foam.
 13. The method of claim 12wherein said gas is present in an amount sufficient to lower the densityof said foam to in the range of from about 10 to about 12 pounds pergallon.
 14. The method of claim 13 wherein said mixture of foaming andfoam stabilizing surfactants in said cement composition is selected fromthe group consisting of a mixture of an alcohol ether sulfateethoxylated with from about 3 to about 10 moles of ethylene oxide and analkyl or alkene amidopropylbetaine and a mixture of an alcohol ethersulfate ethoxylated with from about 3 to about 10 moles of ethyleneoxide, an alkyl or alkene amidopropylbetaine and an alkyl or alkeneamidopropyl dimethylamine oxide.
 15. The method of claim 14 wherein saidmixture of cement composition foaming and foam stabilizing surfactantsis present in an amount in the range of from about 0.1% to about 3% byweight of water in said composition.
 16. The method of claim 15 whereinsaid cement composition further comprises an additive selected from thegroup consisting of calcium aluminate and one or more alkali metalaluminates.
 17. An improved method of cementing a casing string in adeep water offshore formation penetrated by a well bore comprising thesteps of: (a) preparing a cement composition comprised of a hydrauliccement, a water reducing additive comprised of a sulfonatednaphthalene-formaldehyde condensate, a dispersing additive comprised ofthe condensation product of acetone, formaldehyde and sodium bisulfite,a compressive strength enhancing and set retarding additive comprised ofa copolymer of acrylic acid and 2-acrylamido-2-methylpropane sulfonicacid, a set accelerating additive and water present in an amountsufficient to form a pumpable slurry; a gas in an amount sufficient toform a foam and a mixture of cement composition foaming and foamstabilizing surfactants present in an amount sufficient to facilitatethe formation of and stabilize said foam; (b) placing said cementcomposition in the annulus between said casing and said well bore; and(c) allowing said cement composition to set into a hard impermeable masstherein.
 18. The method of claim 17 wherein said hydraulic cement is aPortland or equivalent cement.
 19. The method of claim 17 wherein saidhydraulic cement is selected from the group consisting of API Classes A,C, H and G Portland cements.
 20. The method of claim 17 wherein saidwater reducing additive is present in said composition in an amount inthe range of from about 0% to about 3% by weight of said hydrauliccement in said composition.
 21. The method of claim 17 wherein saiddispersing additive is present in said composition in an amount in therange of from about 0% to about 2% by weight of said hydraulic cement insaid composition.
 22. The method of claim 17 wherein said compressivestrength enhancing and set retarding additive is present in saidcomposition in an amount in the range of from about 0.01% to about 1% byweight of said hydraulic cement in said composition.
 23. The method ofclaim 17 wherein said set accelerating additive is a water solublecalcium salt selected from the group consisting of calcium chloride,calcium nitrate and calcium formate.
 24. The method of claim 17 whereinsaid set accelerating additive is calcium chloride.
 25. The method ofclaim 17 wherein said set accelerating additive is present in saidcomposition in an amount in the range of from about 0.1% to about 4% byweight of said hydraulic cement in said composition.
 26. The method ofclaim 17 wherein said gas is present in an amount sufficient to lowerthe density of said foam to in the range of from about 10 to about 12pounds per gallon.
 27. The method of claim 17 wherein said mixture offoaming and foam stabilizing surfactants in said cement composition isselected from the group consisting of a mixture of ani alcohol ethersulfate ethoxylated with from about 3 to about 10 moles of ethyleneoxide and an alkyl or alkene amidopropylbetaine and a mixture of analcohol ether sulfate ethoxylated with from about 3 to about 10 moles ofethylene oxide, an alkyl or alkene amidopropylbetaine and an alkyl oralkene amidopropyl dimethylamine oxide.
 28. The method of claim 17wherein said mixture of cement composition foaming and foam stabilizingsurfactants is present in an amount in the range of from about 0.1% toabout 3% by weight of water in said composition.
 29. The method of claim17 wherein said cement composition further comprises an additiveselected from the group consisting of calcium aluminate and one or morealkali metal aluminates.
 30. The method of claim 17 wherein saidadditive is calcium aluminate present in said composition in an amountin the range of from about 0.5% to about 5% by weight of said hydrauliccement in said composition.